1. Field of the Invention
The present invention relates to electric power conversion devices such as inverter devices comprised of switching elements and a control circuit for performing a turning-on and off control of the switching elements.
2. Description of the Related Art
A patent document 1, Japanese patent laid open publication No. 2012-139016, has disclosed a three phase inverter device. The three phase inverter device is comprised of switching elements, for example, insulated gate bipolar transistors (IGBTs), a control circuit substrate, direct current (DC) input terminals, a smoothing capacitor and a housing casing. A control circuit is mounted to the control circuit substrate. The control circuit controls the operation of each of the switching elements. The switching elements are connected to a battery through the DC input terminals and the smoothing capacitor. The smoothing capacitor performs a smoothing operation for a DC voltage supplied from the battery, and supplies the smoothed DC voltage to the switching elements. The housing casing accommodates the switching elements, the control circuit substrate, the DC input terminal, and the smoothing capacitor. The DC input terminals are noise sources. For example, switching noise (electromagnetic waves) is generated in the DC input terminals when the switching elements are turned on and off. There is accordingly a possibility of causing incorrect operation in the switching elements when the switching noise is propagated to the control circuit substrate.
In order to avoid this problem, the three phase inverter device has a metal plate which separates the DC input terminals from the control circuit substrate. The metal plate is bent to be arranged between the DC input terminal and the control circuit substrate. The metal plate prevents the propagation of switching noise generated in the switching noise source and suppresses the negative influence of the switching noise on the correct operation of the switching elements.
The inventors of the present invention have proposed a three phase inverter device having an improved structure in which the smoothing capacitor is arranged to face the plate surface of the control circuit substrate. For example, the housing casing of the three phase inverter device has a flat shape in order to miniaturize the whole size of the three phase inverter device.
However, because noise sources such as the DC input terminals are arranged close to the control circuit substrate in the three phase inverter device having the structure as previously described, the incorrect operation of the control circuit is often caused by switching noise propagated on the control circuit substrate. In this case, it can be considered to use the structure disclosed in the patent document 1 in order to reduce the switching noise propagated to the control circuit substrate. Although the technique disclosed in the patent document 1 can reduce the switching noise propagated to the control circuit substrate, this technique requires an additional metal plate in the three phase inverter device in order to reduce the switching noise. Accordingly, this structure increases the manufacturing cost and the whole size of the three phase inverter device.
The problem previously described would be caused in various types of electric power conversion devices such as three phase inverter devices so long as the electric power conversion device performs the switching control operation of the switching elements to convert an input voltage, i.e. a DC voltage to an output voltage, i.e. an alternating current (AC) voltage.